Optical element



Patented June 9, 1925.

UNITED STATES PATENT OFFICE.

KURT PAN'GENBERG, or JENA, GERMANY, ASSIGNOR 'ro THE FIRM can]; znrss, or

, mus, GERMANY.

OPTICAL ELEMENT.

f No Drawing.

To all whom it may mm.-

Be it known that I, KURT SPANGENBERG, a v

citizen of Germany, and residing at Jena, (1ermany,-'have invented anew and useful 5 Optical Element (for which I have filed' an lpplicat-ion in Germany September 12, 1922) of which the following is'a specification.

In the optical glasses hitherto known it has notbeen possible to attain a lower refractive index than n :1,4637 and a smaller colour dispersion than corresponding to the value v=7 0,6. Besides, these values do not even ap pear jointly but the value a 1.4637 is united with the value v:65,6 and the value v=70,6 15 is united with the value n =1,4860. However, according to the present invention it is possible to carry out optical elements of still lower refraction and still smaller colour dispersion by making them of certain, definit/e alkaline fluorides. As with the use for optical instruments it is'not only the optical properties which are decisive but also certain other properties are indispensable as, c. g. the capacity of resistance to the gener- .ally unavoidable moisture ofathe air, of the alkaline fluorides only crystallized fluoride of sodium and crystallized fluoride of lithium may be used. For, these two substances approximately the following values hold good: i

. 7h; v Fluoride of sodium. 1,3257 84,5 Fluoride of lithium 1, 3915 80 As regardsthe relative dispersion these substances suit well to crown glass.

Application filed July 20,

1922. Serial no. 652,843.

, tained fromeasily disposable raw materials,

cannot only replace in many cases the natural fluorsparwhlch is becoming more and more scarce, but in certain cases (e. g

for the correction of spherical errors) they might be even more suitable than fluorspar.

In addition, it is to be anticipated that it' will be possible to attain with optical elements of the aforesaid substances together with such of fluorspar efiects which are *IHOIG favourable than those attained hitherto (0. g. for the achievement of an undercorrection of the spherical errors together with an overcorrectionof the colour-defects).

Although the subjoined claim only deals with fluoride of sodium, it is also intended 1 fluoride of sodium.

KURT 'SPANGENBERG. 

